1. Field of the Invention
This invention relates to the field of facilitating collaborative annotation of a document. The invention is especially suitable for (but not limited to) permitting collaborative annotation of a document by users located at different geographical locations. The invention is also especially suitable for (but not limited to) use with a real-time conferencing system.
2. Description of Related Art
The main problem addressed by a collaborative annotation system is how to enable users located at different locations, for example different geographic sites, to annotate a common document, and to view each other's annotations.
This is especially desirable in a real-time environment, such that the users can work on the document together (for example in combination with a conferencing system, such as a video conferencing system).
U.S. Pat. No. 5,826,025 describes a system which supports collaborative annotations on Web pages. However, the system only permits annotations in the form of character sequences obtainable by a standard computer keyboard. In other words, each user has to enter the annotations using a keyboard.
U.S. Pat. No. 5,781,727 describes a system which permits annotations made by users at remote computers to appear on the displays of other participants. The system can be added to existing document sharing systems such as those described in U.S. Pat. Nos.: 5,220,657; 5,583,993; and 5,781,732. However, the annotations are restricted only to standard shapes, symbols and diagrams similar to those found in a graphics “paint” program.
U.S. Pat. No. 5,897,648 describes a collaborative annotation system which supports handwritten annotations. However, the system requires a special digitizer pen and an x-y digitizer base on which the paper document must be placed so that the annotations can be recorded and digitized. Such apparatus is expensive, and requires considerable desk space making it inconvenient to use. Additionally, all handwritten annotations have to be inputted using the digitizer, and so the system cannot deal with any documents which have already been annotated.